Gl. .^^ 



U. S. DEPARTMENT OF AGRICULTURE. 

BUREAU OF PLANT INDUSTRY— BULLETIN NO. 241. 

B. T. GALLOWAY, Chief of Bureau. 



fHE USE OF ARTIFICIAL HEAT IN CURING 
CIGAR-LEAF TOBACCO. 



BY 



W. W. GARNER, 
Physiologist in Charge of Tobacco and Plant Nutrition Investigations. ^ 



Issued April 23, 1912. 




WASHINGTON: 

GOVERNMENT PRINTING OPPIOE. 

1912. 



%r)0|;n^ 



U. S. DEPARTMENT OF AGRICULTURE. 

BDREAU OF PLANT INDUSTRY— BULLETIN NO. 241. 

B. T. GALLOWAY, CWe/o/ Bureau. 



THE USE OF ARTIFICIAL HEAT IN CURING 
CIGAR- LEAF TOBACCO. 



W. W. GARNER, 

Physiologist in Charge of Tobacco and Plant Nutrition Investigations. 



Issued April 23, 19] 2. 




WASHINGTON: 

GOVERNMENT PRINTING OFFICE, 

1912. 



v( 



\ 



N 



K 






BUREAU OF PLANT INDUSTRY. 



Chief of Bureau, Beverly T. Galloway. 
Assistant Chief of Bureau^ Willam A. Taylor. 
Editor, J. E. Rockwell. 
Chief Clerk, Ja.me.s E. .Toxe.s. 



-|> 



Top.Ai'co AND Pi,A\T-XrTi!rrr()\ Investigation's. 

SCIENTIFIC staff. 

W. W. (Jarner, fhi/siolof/ist in Charfie. 

E. H. Mathewson and G. W. Harri-s, Crop Technolotiists. 

E. G. Beinhart. D. E. Brown. W. M. Lunn, E. G. Moss, and Otto Olson. Aftsistants. 
B. F. Scherffius and .T. S. Cuninjiham, Experts. 
H. A. Allard and C. L. Fouhcrl, Scientific Assistants. 
('. W. Bacon, .Assistant I'ln/siDlonist. 
J. E. Blohm, Special Agent. 

K. M. East, E. K. Ilibshman, W. \V. Green, U. 1'. Cocke, B. (i. .\ndrrson, 'i'rue Ilouser, and 
G. T. McNess, Collaborators. 
241 



my 20 m2 



1:R OF TRAXSMITTAL 



U. S, Depaktment of Agriculture, 

Bureau of Plant Industry, 

Office of the Chief, 
Washington^ D. C, Jamiary 10. 1912. 
Sir : I have the honor to transmit herewith a manuscript entitled 
" The Use of Artificial Heat in Curing Cigar-Leaf Tobacco," by 
Dr. W. W. Garner, Physiologist in Charge of Tobacco and Plant- 
Xutrition Investigations, and to recommend that it be published as 
Bulletin No. 241 of the Bureau series. 

This paper presents the results of investigations which have been in 
progress for several years in the Connecticut Valley relating to the 
nnprovement of present methods of curing cigar tobacco. It has 
been demonstrated that by the use of artificial heat the curing can 
be successfully accomplished during the most unfavorable weather 
conditions, and methods for accomplishing this end are outlined. 

The author desires to acknowledge his indebtedness to Mr. "W. S. 
Pinney, of Suffield, Conn., who has made a study of tobacco curing 
for many years, for his enthusiastic cooperation in these invesiga- 
tions. Mr. Pinney has not only worked out many of the mechanical 
details of applying heat by means of flues, but has thoroughly demon- 
strated b}^ tests conducted on a large scale the value of this method 
of utilizing artificial heat in curing cigar tobacco. 
Eespectfully, 

B. T. (xALLOWAV, 

Chief of Uiirtdii. ■ 
1^41 - 



CONTENTS. 



Introduction 7 

Changes in the properties and composition of the tobacco leaf while curing 8 

The necessary conditions for good curing 9 

Pole-sweat, or pole-burn 9 

How to prevent pole-sweat 10 

The effect of heat applied during the ciu-ing process on the quality of tobacco. . 12 

Forcing the cure by the use of artificial heat 13 

Methods of applying artificial heat 15 

The use of charcoal in curing 16 

The use of flues in curing 18 

Barns adapted to the use of heat in curing 23 

Summary 24 

241 

5 



ILLUSTRATIONS 



Page. 
J^iG . 1 . Sketch showing the arrangement of furnaces and flues in a bam adapted 

for curing yellow tobacco 19 

2. Type of concrete furnace, cast in sections, for use in applying artificial 

heat through flues, devised by W. S. Pinney, Sufiield, Conn 20 

3. Furnace and flue in position 21 

4. Moderate-sized barn with low, flat roof and ventilator extending along 

the peak of the roof, especially ada})ted for the use of artificial heat 

in curing 24 

241 

e 



B. r. I.— 722. 

THE USE OF ARTIFICIAL HEAT IN CURING 
CIGAR-LEAF TOBACCO. 



INTRODUCTION. 

The term '• curing," as applied to tobacco, is sometimes used to 
include all of the processes to which the leaf is subjected after it has 
been harvested in preparing it for the manufacturer. There are 
thus included three more or less distinct processes, namely, .the cur- 
ing proper (frequently spoken of as •" barn curing '') , the fermentation 
process, and the aging process. The term as used in this article re- 
lates only to the first-mentioned process, in which the tobacco is pre- 
pared for fermentation. 

In general, it can be said that the cigar-tobacco industry has 
reached a high plane of development in this country. In some sec- 
tions at least, highly intensive methods are applied, the soil is heavily 
fertilized, the most approved cultural methods are used, and the 
growing crop from beginning to end receives the closest attention. 
Nevertheless, the methods of curing this type of leaf now in use must 
be regarded as crude when compared with those followed with some 
other types, notably the bright flue-cured tobaccos, notwithstanding 
the fact that with this latter type the general cultural methods are 
far from satisfactory. It is true that great progress has been made 
in the construction of barns for curing cigar leaf and many of those 
now in use in the wrapper-growing sections are models of perfection, 
but the method of curing which has been in almost universal use in 
sections growing cigar tobacco is air curing; that is, no artificial 
heat is used during the progress of the process. As a result the pre- 
vailing conditions in the curing barn are more or less subject to all 
the variations of the outside weather conditions and good curing is 
largely a matter of chance. Furthermore, the fact that there has 
been no satisfactory means of controlling the conditions in the curing 
barn has made it impossible for growers to make much progress in 
learning just what these conditions should be in order to secure the 
best results in curing. 

The growers of western Florida have long followed the practice of 
utilizing open fires made on the floor of the barn for reducing the 
27727°— Bull. 241—12 2 7 



8 USE OF ARTIFICIAL HEAT IX CURING CIGAR-LEAF TOBACCO. 

excessive moisture during wet or cloudy weather; This procedure, 
which has been more recently applied in connection with the growing 
of wrapper leaf under artificial shade, effectually prevents injury 
from the disease knoAvn as pole-sweat. Charcoal and well-seasoned 
Avood are used as fuel, the fires being so managed as to produce as 
little smoke as possible. More recently open charcoal fires have 
come into extensive use in the Connecticut Valley in connection with 
the shade-tobacco industry, having been introduced by Mr. M. L. 
Floyd, of the Connecticut Tobacco Corporation. With these excep- 
tions, however, it is only in rare instances that artificial heat is re- 
sorted to in curing cigar tobaccos. 

CHANGES IN THE PROPERTIES AND COMPOSITION OF THE 
TOBACCO LEAF WHILE CURING. 

That the properties of the tobacco leaf are greatly changed in the 
curing is w^ell known to every grower, but the changes in composition 
which thus alter these properties and the necessary conditions for 
bringing about these changes are little understood. The leaf when 
harvested contains from 70 to 80 per cent of water, the greater por- 
tion of which is lost by evaporation during the curing. Nevertheless, 
curing involves much more than the mere drying of the leaf, for a 
leaf can be completely dried in a few^ minutes by applying sufficient 
heat and such a leaf does not show the properties of cured tobacco. 
In addition to the loss of water there is a marked loss in weight of 
other constituents of the leaf, usually amounting to 15 to 30 per 
cent of the weight of the cured j^roduct. Thus, a hundred pounds of 
green tobacco, containing, say, 75 pounds of water, will lose 4 to 7 
pounds of dry matter in curing, in addition to losing more than 70 
pounds of the w^ater. 

It is not necessary to enter into a consideration of the exact char- 
acter of the changes involved in the loss of dry matter, but it can be 
easily demonstrated that these changes are dependent on the activities 
of the living cells of the leaf. If a green leaf be killed wdth chloro- 
form, heat, or other means, such a leaf can not be cured. Curing, in 
fact, consists essentially in subjecting the living leaf cells to a process 
of gradual starvation under proper conditions. The loss in dry 
matter represents largely the material consumed by the cells in an 
effort to maintain life as long as possible and is analogous to the loss 
in weight of animals undergoing starvation. The evidence of these 
changes in composition brought about by the starvation and final 
death of the leaf tissue consists in the change of the green color to 
yellow and, finally, to brown, the change in texture and the develojo- 
ment of elasticity, and other properties of cured tobacco. 

241 



POLE-SWEAT, OR POLE-BURN. 9 

THE NECESSARY CONDITIONS TOE, GOOD CURING. 

It is quite jDOSsible to dry the tobacco leaf without curing it, and it 
is also largely possible to cure the leaf without drying it. The two 
processes may or may not go hand in hand, depending on whether 
the existing conditions favor both processes. In practice the problem 
is to dry the leaf under such conditions as will best develop the de- 
sirable qualities of cured tobacco. It is to be remembered that if the 
living cells of the leaf are killed prematurely^ the curing is stopped 
once for all, although the drying may continue. Under ordinary 
conditions the leaf is killed by the loss of water, so it is essential that 
too rapid drying be avoided in order to afford an opportunity for the 
curing changes to take place. On the other hand, if the drying is too 
slow or is delayed too long the curing proceeds too far. The rate of 
drying is therefore one of the principal factors in good curing. 

In addition to loss of water, the leaf cells may also be prematurely 
killed by excessively low or high temperatures or by mechanical in- 
juiy, such as bruising the tissue in harvesting. No portion of a leaf 
which is prematurely killed by these or other means can be success- 
fully cured. It follows that tobacco which is subjected to frost, freez- 
ing temperatures, or too high temperatures when artificial heat is 
applied, especially in the first stages, can not be properly cured. 

Aside from the premature killing of the leaf tissue by extremes 
of heat or cold, the temperature plays a vei*y important part in 
affecting the rate of curing. The curing proceeds very slowly or 
is stopped completely at temperatures below 00° F., while the dry- 
ing may go on rapidly if the air entering the barn is dry; in other 
words, the leaf under these conditions is likely to dry without curing. 
On the other hand, curing proceeds very rapidly at 80° to 100° F.. 
while the rate of drying can be controlled by regulating the humidity 
in the barn. 

It will thus be seen that the necessary conditions for good curing 
are that the tobacco be placed in the barn in sound condition, that 
the temperature be kept sufficiently high to allow the curing changes 
to proceed normally, and that the rate of drying be controlled by 
regulating the humidity so as to avoid either too rapid or too slow 
drying. The matter of properly regulating the humidity in the 
curing barn is discussed m the succeeding paragraphs. 

POLE-SWEAT, OR POLE-BURN. 

Pole-sweat, or pole-burn, which is so well known in those tobacco- 
producing sections where artificial heat is not used in curing, is one 
of the results of too slow drying in the more advanced stage of 
curing. Pole-sweat is nothing more than the rotting or decay of the 
leaf and is analogous to the ordinary decay of organic matter of 

241 



10 USE OF ARTIFICIAL HEAT IN CURING CIGAR-LEAF TOBACCO. 

either animal or vegetable origin. It is important to understand this 
fact fully, for it renders it an easy matter to recognize the stage of 
the curing when pole-sweat is to be looked for and points clearly to 
the proper remed}'. The decay of the leaf is due to micro-organ- 
isms, or "germs," which are active only at moderate temperatures 
and in the presence of an abundance of moisture. There will be 
little or no pole-sweat so long as the temperature remains below 00° 
F. or the relative lunnidity is less than 85 per cent. 

It is alsp important to remember that these organisms feed only 
on dead or dying tissue. So long as the leaf tissue remains alive 
there can be no pole-sweat. Under ordinary conditions the appear- 
ance of the yellow color on the leaf indicates that the cells are reach- 
ing the dying stage; hence, this is the stage where pole-sweat is to 
be expected. It is sure to develop if the temperature is warm and 
if the humidity in the barn is high. It will be seen that the most 
favorable conditions for curing are those which lead to pole-sweat, 
but it is also true that the real curing is practically completed when 
the stage for pole-sweat is reached, and these facts open the way for 
a simple remedy against the disease. 

Most growers are familiar with the so-called "strutting" of the 
leaf as a forerunner of pole-sweat, which is a stiffening of the midrib 
and veins, causing the previously wilted leaf to stand out somewhat 
like an opened umbrella. This strutting has no direct connection 
with pole-sweat except that both are due to the same cause, namely, 
excessive humidity. 

Stern-rot — that is, decay of the midrib — is also likely to appear in 
the later stages of the curing when the drying is checked by excessive 
humidity. This trouble is more common when the tobacco is har- 
vested by picking the leaves from the stalk. In the later stages of 
curing, after the leaf has turned brown, damage may result from 
drops of moisture collecting on the leaf when the drying is checked, 
thereby causing discoloration, even though pole-sweat does not 
develop. 

HOW TO PREVKNT POLE-SWEAT 

Wliile it is true that pole-sweat is held in check by temperatures 
lielow 60° F., it is to be remembered that the curing is also stopped 
at low temperatures, while the drying of the leaf may continue. The 
only practicable remedy lies in the proper control of the humidity 
in the bam ; in other words, there must be adequate means of 
removing the excessive moisture during periods of wet weather. 

Many growers have an impression that ventilation is effective in 
controlling this disease, but it can be easily seen that if the outside 
air is saturated with moisture ventilation alone, however thorough it 

241 



POLE-SWEAT, OR POLE-BURN. 11 

may be, can not possibly reduce the moisture in the barn. ]Moreover, 
the degree of crowding together of the tobacco in the barn has an 
influence only in so far as this affects the moisture of the air, and a 
single leaf of tobacco placed in the barn ^Yill rot the same as if the 
barn were completely filled, provided the temperature and moisture 
conditions favor pole-sweat. To reduce the moisture in the bam in 
wet w^eather the relative humidity of the air in contact with the 
tobacco must be reduced, and the only practicable means of accom- 
plishing this is by the use of artificial heat combined with properly 
regulated ventilation. The capacity of the air^ for holding moisture 
is greatly influenced by the temperature. For each increase of tem- 
perature of 18 or '20 degi-ees the capacity is cloubled; so that, for ex- 
ample, if the temperature of a given volume of saturated air is 
raised from 50° to 70° F., the relative humidity drops from 100 per 
cent to 50 per cent. It will be seen, therefore, that if sufficient heat 
is applied to raise the temperature in the barn 15 or 20 degrees, and if 
the air is constantly rencAved by ventilation, the relative humidity will 
be kept down to only 50 or GO per cent. Under these conditions the 
tobacco will dry even more rapidly than is the case on a warm, bright 
sunshiny day. 

To so regulate the temperature and ventilation as to avoid pole- 
sweat and at the same time insure the best possible curing is a matter 
for which definite instructions can not be given, for the reason that 
so much depends on the varying outside weather conditions and on 
the character and quantity of the tobacco in the barn. Our experi- 
ments in the Connecticut Valley have shown conclusively, however, 
that pole-sweat can be easily and completely controlled by the com- 
bined use of heat and ventilation, no matter how unfavorable the 
weather may be, and it is only a matter of experience to determine the 
quantity of heat and the amount of ventilation required in any given 
case. To be assured of success under all conditions means must be 
available for raising the temperature in the barn, which must be 
reasonably tight, 15 to 20 degrees above the outside temperature when 
moderate ventilation is used. Where the heat is applied before pole- 
sweat begins it will usually be necessary to use only moderate amounts 
if the heating is continued until the tobacco has passed the danger 
point, whereas if the disease has already gained headway more dras- 
tic heating is required to check it promptly. 

The mistake must not be made of apjolying too little heat or api^ly- 
ing it for an insufficient length of time, for this will only aggravate 

1 It should be stated hei'o. once for all, that, strictly speaking, the air can not be con- 
sidered as having capacity for moisture, for the water vapor is in reality merely mixed 
with the air. It would be more correct to speak of a given space as being saturated with 
moisture, but the common phraseology is so firmly established and so much more readily 
comprehended that for uur purposes it seems desirable to retain it. 
i;41 



12 USE OF ARTIFICIAL HEAT IN CURING CIGAR-LEAF TOBACCO. 

the trouble. In no case where there is real danger of pole-sweat 
should the temperature in the barn be allowed to remain less than 
10 to 12 degrees above that of the outside air, and moderate ventila- 
tion is likewise essential. The condition of the tobacco is the proper 
guide in all cases, and it is important to examine the leaf at intervals 
in all parts of the barn, and particularly in the upper tiers. The 
heated air tends to rise, and sufficient heat must be used to reach the 
top of the barn : otherwise the moisture from the tobacco in the lower 
tiers is merely carried upward and deposited on -the cooler tobacco 
nearer the top. 

THE EFFECT OF HEAT APPLIED DURING THE CURING PROCESS 
ON THE QUALITY OF TOBACCO. 

In considering the use of artificial heat in curing cigar tobacco 
the question naturally arises as to the effect of the heat on the quality 
of the cured leaf. As a matter of fact, it is quite possible so to 
apply the heat as to produce no artificial condition; that is, it may 
be applied only when the weather is unfavorable, and in such a way 
as to create those temperature and moisture conditions which would 
prevail in the barn when the weather is just right for curing. In 
this case the principal use of the heat would be to prevent pole-sweat, 
and there is no reason to suppose that the result of the curing would 
be different from that obtained in favorable weather without the 
use of artificial heat. 

On the other hand, the curing may be forced by the use of heat so 
as to hasten the process and materially affect the quality of the cured 
leaf. Bearing in mind that the rate of drying and the rate of curing 
may or may not go iiand in hand, it is plain that uniformly satis- 
factory results in tobacco curing can never be assured until efficient 
methods of regulating t^le temperature and moisture in the barn are 
followed. Artificial heat not only furnishes a means of securing the 
most favorable temperatures for curing, but when combined with 
ventilation also constitutes the only practicable means of. controlling 
the humidity. 

The rate of curing greatly increases with a rise in temperature, and 
in general more thorough curing is obtained at higher temperatures, 
provided the leaf is not dried too rapid l3\ It follows that artificial 
heat when properly applied is highly favorable to the quality of 
cigar tobacco, for thorough l)arn curing is essential to the best de- 
velopment of flavor, aroma, and elasticity and, to a lesser degree, of 
color in the sweating or fermenting process. 

Artificial heat probably shows the greatest effect on the color of the 
cured leaf. Heat in the presence of sufficient moisture greatly hastens 
the rate of curing, but when used in conjunction with ventilation it 
also greatly increases the rate of drying. At given temperatures the 

241 



FORCING THE CURE BY THE USE OF ARTIFICIAL HEAT. 13 

extent of the changes in color occurring during the curing are con- 
trolled by the amount of moisture in the leaf, so that the use of heat 
and ventilation combined makes it possible to control to a certain ex- 
tent the colors obtained. We have found in the course of our ex- 
periments that not only the depth of the color, but also its character, 
can be largely controlled by regulating the temperature and ventila- 
tion. Under the present method of curing cigar-wrapper tobacco, 
particularly when the leaf is cured on the stalk, the final color of the 
bright wrappers is normally a clear cinnamon brown, free from any 
greenish cast, but generally showing more or less tendency toward a 
reddish cast. The present demand is for a wrapper of rather dull 
finish, showing the lighter shades of brown overlaid with a faint olive 
but absolutely free from red. The recent rapid development in the 
Connecticut Valley of the method of harvesting by picking the leaves 
from the plant is due primarily to this demand for a wrapper of 
" Cuban finish." It has been demonstrated that artificial heat is an 
important factor in obtaining the best curing with this type of leaf. 

FORCING THE CURE BY THE USE OF ARTIFICIAL HEAT. 

The two most important reasons why artificial heat should be used 
in curing practically all tobaccos are that (1) this affords the only 
practicable means of preventing the decay of the leaf caused bj^ exces- 
sive moisture during wet weather and (2) tobacco does not cure prop- 
erly at low temperatures, however favorable the weather may be 
otherwise, a. fact of special importance in northern tobacco districts. 
In the case of cigar-wrapper leaf another important consideration is 
that proper control of the moisture in the bam, which can only be 
accomplished by the use of heat combined with ventilation, is the 
most efficient means of securing desirable colors in the cured product. 
Where no heat is used it frequently happens that even after the cur- 
ing is largely completed wet periods of weather bring the tobacco into 
such moist condition that the color is greatly darkened and the quality 
of the tobacco otherwise injured, while if cold w^eather prevails dur- 
ing the curing the leaf simply dries without otherwise developing the 
desired properties of cured tobacco. The curing of cigar tobaccos can 
never be placed on a satisfactory basis until the process has been 
rendered largely independent of weather conditions by the combined 
use of artificial heat and ventilation. 

During the first stage of the curing, in which the yellow color de- 
velops, the principal value of the heat is to maintain a favorable 
temperature in the barn, and during this period care must be taken to 
avoid too rapid drying. It is evident that the barn must be reason- 
ably tight, so as to prevent the rapid escape of the heat and moisture. 
On the other hand, the barn must have proper means of ventilation 

241 



14 USE OF ARTIFICIAL HEAT IN CURING CIGAR-LEAF TOBACCO, 

(luring wet weather, otherwise the drying will be checked and there 
will be danger of pole-sweat when the second stage of the curing 
is reached. If the outside temperature is below G0° F,. heat should 
be applied; if the w-eather is clear, little, if any, ventilation is 
needed, while in wet weather more ventilation is necessary. The aim 
should be to keep the temperature in the barn above 70° F. and to 
regulate the ventilation so that the tobacco will dry slowly until it 
is pretty well j'ellowed. The leaf will cure satisfactorily at any 
temperature between 70° and 100° F., and the exact temperature 
to be maintained in the barn will depend on outside weather con- 
ditions. To prevent too rapid drving in cold, dry weather, even with 
the minimum amount of ventilation, the inside temperature should 
not be much more than 10 or 12 degrees above that of the outside 
air, while in wet weather a difference in the inside and outside tem- 
peratures of about 15 degrees is desirable, the ventilation also being 
increased. 

With favorable temperatures the necessary changes effected in the 
curing proceed much faster than is commonly supposed, even though 
this is not apparent to the eye. so that Avhen heat is applied, if the 
leaf does not become dry during, say. the first 48 hours, there is no 
danger of injuring the color thereafter by rapid drj-ing. Under 
these conditions the green color left in the leaf disappears as soon 
as the cured tobacco comes into case a few times; in fact, in our ex- 
periments the best colors have been obtained from tobacco which was 
still quite green Avhen the curing proper had been completed. 

After the first stage of the curing has been completed — that is, 
when the leaf has yellowed sufficiently — whether or not the further 
use of heat is desirable depends mainly on the prevailing weather 
as to humidity. This is the period for pole-sweat, and if there is 
much damp weather the heating will need to be continued, while 
Avith favorable weather the curing can be completed Avithout the 
further use of heat. In any event, however, the tobacco at this stage 
should be allowed to soften well before proceeding with the drying, 
and it is well to allow the leaf to come into good case from time to 
time until the midrib is cured. If, because of lack of barn room or 
other reasons, it is desired to hasten the second stage of the curing, 
heat can be freely used without fear of injuring the quality of the 
tobacco. 

While it is true that the occasional softening of the tobacco during 
the second stage of the curing greatly improves its appearance, grow- 
ers as a rule do not fully appreciate the serious injury to the color 
caused by allowing the cured tobacco to become too damp. Each 
time a cured leaf becomes damp the color is not only darkened, but 
loses in clearness and, besides, the tobacco undergoes a sort of cold 

241 



METHODS OF APPLYING ARTIFICIAL HEAT. 15 

sweat which interferes with its normal fermentation in the packing- 
house. This injury can be easil}^ avoided by drying out the tobacco 
with artificial heat during wet or damp weather. 

The suggestions here outlined regarding the use of artificial heat 
in curing haA'e been worked out by experiments with wrapper leaf 
harvested by picking the leaves from the stalk, but the same princi- 
ples can be applied to curing on the stalk, the main difference being 
that the curing Avill necessarily require more time. In our experience 
with picked tobacco, as has already been stated, in addition to avoid- 
ing direct injury to the quality of the leaf from unfavorable weather 
conditions, it has been found that the use of artificial heat gives the 
desired brown color, free from red and of dull finish. 

METHODS OF APPLYING ARTIFICIAL HEAT. 

We have pointed out the necessity of having available some suitable 
means of applying artificial heat, in order to control the temperature 
and moisture conditions in the barn, if the best results in curing are 
to be obtained. This brings us to a consideration of practical meth- 
ods of applying heat and the requirements which these methods must 
meet. In cold, dry weather the curing ceases but the drying contin- 
ues, while in wariu, wet weather the curing proceeds rapidly and the 
leaf may even decay because the drying is stopped. A practical 
heating system must, therefore, be capable of controlling both tlie 
temperature and humidity so as to avoid these extremes. 

No heating sj^stem will give satisfactory results in a barn wdiich is 
not reasonably tight, for the temperature in such a barn can not be 
raised sufficiently without drying the tobacco too rapidly. On the 
other hand, a system of ventilators which can be opened and closed at 
Avill is necessary for the removal of the excessive moisture in the barn 
in wet weather. If there is no ventilation the air in the barn soon 
becomes saturated, and heat alone is of little or no value in this case. 
AMien artificial heat is used it is not desirable in filling the barn with 
tobacco to leave open spaces or vents from top to bottom, for these 
merely serve as channels for the escape of the heat to the top of the 
barn, while to be effective it must be forced to pass through the 
tobacco. 

The heating system must have sufficient capacit3\ A little heat is 
frequently worse than none, particularly in the control of pole-sweat. 
Experience has shown that a satisfactory system must be capable of 
maintaining the temperature in the barn from 15 to 20 degrees higher 
than that of the outside air when moderate ventilation is used. It 
is only necessary to maintain this difference in temperature, however, 
when there is danger from pole-sweat, and under ordinary conditions 
a difference of 10 or 12 degrees between the inside and outside air is 

241 



16 USE OF ARTIFICIAL HEAT IN CURING CIGAR-LEAF TOBACCO. 

sufficient. The heat must be applied at the bottom of the barn and 
must be evenly distributed in order that, so far as possible, all of 
the tobacco may receive the same amount. 

As is well known, artificial heat has long been used in curing 
certain types of export and manufacturing tobaccos. There are 
essentially two methods of applying the heat. In the case of the 
so-called dark fire-cured export tobacco open fires are made on the 
floor of the barn and the smoke is allowed to pass up through the 
tobacco, thereby imparting a characteristic odor and taste to the 
leaf. No heat is applied for the first few days and thereafter the 
fires are maintained only at intervals, so that the tobacco is only 
partially cured with artificial heat. In the case of flue-cured manu- 
facturing tobacco, the heat is introduced by means of furnaces fitted 
with a system of flues through which the heat is distributed. This 
method differs from fire curing in that the smoke does not come in 
contact with the tobacco and the heat is applied continuously 
throughout the curing. The process is completed in from three to 
five days. In flue curing, the temperature can be controlled with 
exactness, and this is decidedly the most perfect system of curing 
now in use. In both flue curing and fire curing wood is the fuel 
used. 

It has already been stated that open fires have long been used in 
curing cigar tobacco in western Florida, and both wood and charcoal 
have been used as fuel. In curing shade-gTOwn cigar- wrapper leaf 
in the Connecticut Valley open charcoal fires are quite generally used. 
The application of open fires and of heating by means of flues is 
considered in the following paragraphs. 

THE USE OF CHARCOAL. IN CURING. 

The evident points in favor of open fires as a source of heat in curing 
are simplicity and cheapness, provided the fuel used is not expensive. 
WHiere wood can be used this is the cheapest method of applying 
heat, since wood is in most cases still a comparatively cheap fuel 
and open fires require almost no special equipment. Charcoal is 
generally preferred for curing cigar tobacco, however, for the rea- 
son that it burns with very little smoke. On the other hand, char- 
coal is one of the most expensive of fuels and the supply is limited 
and uncertain. It is an established fact that even cigar-wrapper 
leaf is not injured by small quantities of smoke, so that thoroughly 
seasoned wood, corncobs, and similar materials which burn with but 
little smoke can be used successfully in an emergency. Of course, 
any material which burns with dense smoke will cause serious dam- 
. age by discoloring the leaf with soot. Coal and coke can not be 
used for open fires because of injurious gases, mainly sulphur dioxid, 
formed in combustion. 

241 



METHODS OF APPLYING ARTIFICIAL HEAT. 17 

One of the principal difficulties to be met iu using open fires is in 
securing an even distribution of the heat. The tobacco hanging di- 
rectly over the fires will be overheated, while that between the fires 
is not likely to receive enough heat. Evidently a large number of 
small fires is better than a few larger fires, and they should not be 
more than 6 or 8 feet apart each way. It will be seen at once, how- 
ever, that the labor required in taking care of the larger number of 
fires will be greatly increased. The small fires require close atten- 
tion to keep them going and to avoid the danger of burning the 
barn. If the bottom tier of the barn is filled the tobacco hangs so 
near the ground that the fires are not easily accessible. In any case 
the tobacco hanging immediately above the spots chosen for the 
fires must be removed before these are started. Small heaters are 
occasionally used for burning charcoal, but these are of doubtful 
value except that they lessen the danger of accidental fires, and the 
same may be said of small pits dug in the floor of the barn, which 
have been used by some. Deflectors of various kinds are frequently 
suspended above the fires to secure a better distribution of the heat, 
and these are serviceable, but less so Avhen constructed of metal, be- 
cause they then transmit the heat very readily. Tliey are most effi- 
cient when flat or having the shape of an inverted cone. 

Open charcoal fires have thus far been used mainly in curing shade- 
grown tobacco, all of which is harvested by picking the leaves from 
the stalk. The method commonly used is to keep the fires going for 
about three days or until the leaf is pretty well yellowed, after which 
no heat is used Except t() prevent damage from pole-sweat in wet 
Aveather. During this period the approximate range of temperature 
in the barn is from 80° to 100° F., depending, of course, on the out- 
side weather conditions. As a rule, the barns are kept tightly closed 
during the firing to prevent the tobacco from drying too rapidly. 
The roof of the barn being covered Avith shingles and therefore 
affording considerable ventilation and this class of tobacco being 
very light in body make it possible to dispense with ventilators on 
the peak, although these are undoubtedly very desirable in northern 
latitudes, as, for example, in the Connecticut Valley. The quantity 
of charcoal required for curing shade-grown tobacco will naturally 
depend very much on weather conditions, but with normal seasons 
there will usually be required from 200 to 300 bushels for a barn 
holding 5 acres of tobacco. "With unfavorable weather conditions 
much larger quantities will be needed. 

For curing ordinary picked tobacco, particularly the broadleaf, 
which is especially liable to develop pole-sweat, much more fuel will 
be required because of the greatly increased amount of water to be 
removed from the barn. For curing on the stalk still more heat a\ ill 
be required if the curing is to be forced, as is done with the shade- 
i;4i 



18 rSE OF ARTIFICIAL HEAT IN CURING CIGAR-LEAF TOBACCO. 

oTown leaf, and it is uoublfiil whethor charcoal could be used except 
at prohibitive cost unless the heat is employed merely to temporarily 
Avard ort" i)ole-sweat. 

THE USE OF FLLTES ]N ( I^RING. 

Because of the difficulties attending the use of charcoal fires for 
forciuir the cure of cigar tobaccos, more particularly the ordinary 
picked and stalk-cured types, Avhich have been pointed out previously, 
experiments have been conducted during the past fcAv years in the 
Connecticut Valley with a view to devising a more economical and 
satisfactory method of applying heat. The possibilities of steam 
heating were first investigated, but it was found that such a system 
is impracticable because of its cost. Attention was next turned to 
the use of flues, such as are employed with other types of tobacco, 
and with unich better success. 

As shown in figure 1, the heating system used in flue-curing dis- 
tricts consists of sheet-iron pipes 10 to 15 inches in diameter, leading 
from furnaces placed at one end of the barn. The flues extend across 
the barn and in returning pass out through the side of the barn, with 
a short smokestack at the end. It will be observed that the flue- 
curing barns are quite small, so that the heat is uniformly distributed. 
The aim of our ex])eriments has been so to modif}^ this method of 
heating as to make it applicable to the curing of cigar tobacco. 

One of the first changes necessary in adapting this system to cigar 
leaf is that the furnaces shall be placed wholl}^ on the inside of the 
barn. This jjrevents unnecessary loss of heat, greatly reduces the 
(•anger of setting fire to the barn, and ])rotects the fire box from being 
Hooded during rainy weather. Since the furnaces need to be set up 
l^ermanently, they nuist be placed in the ground in order that they 
!-hall not interfere with the work of handling the tobacco and also 
that the necessary grade can be given the flues. 

Since the high temperatures used in the flue-curing districts are 
n.ot needed in curing cigar tobacco, the flues should not l)e so large. 
Experience has shown that those having a diameter of S inches are 
([uite satisfactory. In the flue-curing districts the flues are made of 
light-weight black sheet iron antl will last for manj' years, but in the 
Connecticut Valley it has been found that such flues Avill scarcely last 
more than (me season. Galvanized iron of No. 24 gauge is recom- 
mended as a satisfactory material for consti'ucting durable flues. 
Flues of this material will weigh something less than 3 pounds jier 
foot. To facilitate setting up the flues and to avoid the danger of 
fire from loose joints the short pieces of jupe should be riveted to- 
gether into long sections. It is important to have the open joints of 
these long sections made so tliat they can be easily connected, and tliey 
should be i)rovided with " boot strajis " for tying together securely 

^41 



METHODS OF APPLYING ARTIFICIAL HEAT. 



19 



with wire. The joints ordinarily made l)y the manufacturer fit so 
tightly that it requires much time and patience to put them together. 
Thus far wood is the only fuel which has been found suitable for 
heating- the fines, and the furnaces have been designed more particu- 
larly for this fuel. In the system which has l)een dcA^eloped the 16- 
foot sections formed by ])osts. frames, and girders set up across 
the bai'u and known as "bents." are taken as the unit, so that each 




Fi(i. 1. — Sketch showing the aiTanseiiient of furnaces niul IUk's in a barn a(lai)t<'d for 
curing yellow tobacco : F, V, Brick furnaces ; .1, B, V, D, sheet-irnn flues. 

section, or bent, requii'es an independent furnace and set of flues. 
The furnace, which is set in the ground, should be not less than 5 feet 
long and about 10 inches wide, inside measurement. The top should 
slope upward from al)out K) inches at the front to, say, 2G inches at 
the back. The sides and the closed end may be made by laying a 
single thickness of brick without cement of any kind along the sides 
of the pit dug for the purpose, sheet iron fitted with a collar fo'- re- 
ceiving the end of the flue and covered with :! or ?> inches of soil 

1'41 



20 



USE OF ARTIFICIAL HEAT IN CURING CIGAR-LEAF TOBACCO. 



servino; as a top. Such a furnace, however, is not durable and is 
comparatively expensive. 

A very cheap and desirable type of furnace, made of concrete cast 
in sections, is shown in figure 2. Sand and trap rock were used in 
casting these furnaces and the formula used was that ordinarily em- 
ployed for mixing '' strong " concrete. The top, sides, and end are 
all 4 inches thick and of the dimensions given in the preceding para- 
graph. The sides are cast with a 2 by 4 inch notch at the rear end for 
receiving the back. The top is reenforced with steel and is provided 




Fig. 2. — Type of concreto turiiace, cast in sections, for sisc in applyini; artificial heat 
through flues, devised by W. S. Pinney, Suffi'eld, Conn. : «, Side of furnace, with sloping 
upper edge and recess in rear end for receiving the end of furnace ; h, c, top, with 
tapered opening at rear end for receiving end of fine. 

with an opening, tapering dowuiward, G inches from one end for re- 
ceiving the end of the flue. The top is cemented on at the time of 
setting up the furnace. The sections of the furnace are heavy, and 
should be cast in the barn in which they are to be used. If the sand 
and rock can be had near at hand a furnace of this type would cost 
only about $1.50, exclusive of labor. In tests during the past season 
these furnaces gave very satisfactory results, and there is reason to be- 
lieve that if properly made they will prove very durable. 

In the system of heating which has l)een developed with the bent 
as the unit, figure 3 shows the best method which has been devised 

241 



METHODS OF APPLYING ARTIFICIAL HEAT. 



21 



for setting up the flues. The furnaces may be made to run either 
lengthwise or crosswise of the barn. They are all placed on one side 
of the barn, preferably on the north or west side. To prevent the 
excessive radiation of heat from the front end of the furnace the 
lower portion of the opening should be kept closed. This can be con- 
venientl}' done by means of a piece of L-shaped sheet iron, of the 
width of the furnace, which will close about one-half the mouth of 
the furnace. By closing the lower portion the air is forced to enter 
through the upper portion of the opening, Avhich does not interfere 
with the draft but prevents the escape of heated air from this end of 
the furnace. 




Pig. 3. — Furnace and flue in position. At a,, a T-spctlon may be inserted, the open end of 
which pas.ses out of the sido of tho barn, thus preventing a bacl< draft when the wind 
blows into the end of the flue. A separate furnace and set of flues, as shown, are 
required for each bent of the barn. 

The first section of the flue running across the barn from the fur- 
nace can Ix' riveted together into a single piece, while the return por- 
tion can be made of two sections, exclusive of the upright bend near 
the point of exit. This rise at the outer end of the flue is to facilitate 
passing from one furnace to the other and also to secure a better draft 
in the pipe. The elbow on the end is not essential, but is helpful in 
windy weather, as it can be turned so that the open end is away from 
the wind. The best method of supporting the flues is by means of a 
light-weight chain and small S-hooks suspended from the tier poles, 
making it possible to regulate quickly the grading of the flues. About 
36 feet of chain are required for each bent. 

241 



22 USE OF ARTIFICIAL HEAT IN CURING CIGAR-LEAF TOBACCO. 

The system set up as described works very satisfactorily, except 
Avhen there is a strong wind blowing directly into the open end of 
the flue. In this case the flues can not be made to draw. This diffi- 
culty is overcome by using a T-section, fitted with a damper, for 
connecting the return portion of the flue with the end portion — that 
is, at the corner farthest removed from the furnace (see fig. 3, ^1). 
This section will automatically check the back draft caused by the 
wind blowing into the open end of the pipe by furnishing an exit 
for the surplus smoke. The end portion of the flue connecting the 
two runs across the barn can be riveted together into one section, in- 
cluding the ell)ow at one end and the T-piece at the other. 

With a properly constructed barn this system of heating is easily 
capable of maintaining a temperature 20 degrees above that of the 
outside air. It is estimated that from 1 to 2 cords of wood will be 
required for curing an acre of picked tobacco. Some idea of the rel- 
ative cost and heating value of w^ood as compared with charcoal can 
be had from the following data: The average weight per cord of 
wood of various kinds, such as oak, hickory, pine, chestnut, etc., is 
about 3,000 pounds, vnelding about 32 bushels of charcoal, which 
weigh approximately TOO pounds. The quantity of heat obtained 
from 3 pounds of Avood is approximately equal to that obtained from 
2 pounds of charcoal, so that a cord of wood will yield about three 
times the quantity of heat obtained from the same quantit}^ of wood 
after being converted into charcoal. The present price of charcoal 
in the Connecticut Valley is equivalent to a price of $12 to $15 per 
cord for wood. It is considered that the system of heating with flues 
which has been outlined will cost, complete, about $20 per bent, or, 
approximately, $35 per acre. The equipment with minor repairs will 
last many years, and it has been shown that it may pay for itself in 
a single season of bad curing weather. 

It has been conclusively proved by Mr. W. S. Pinney and others 
through tests carried out on a large scale in the Connecticut Valley 
(hu'ing the past two years that this system not only removes all danger 
from pole-sweat, but produces tobacco of the highest quality in all 
respects, particularly when applied to tobacco harvested by picking 
or priming the leaves. It is very probable thai the method of con- 
structing and arranging the furnaces and flues which has been de- 
scribed will be materially improved upon, and there would seem to 
be possibilities in developing a plan involving the use of one or more 
central smokestacks or chimneys extending through the roofs, into 
which the 'various flues can be led. What it is desired to emphasize 
more particularly is the fact that it has been convincingly demon- 
strated that the use of flues for applying artificial heat affords the 
best method yet devised for curing cigar tobacco, especially for cur- 
ing the picked leaf. 

241 



BARNS ADAPTED TO THE USE OF HEAT IN CURING. 23 

111 view of the fact that wood is not always easily obtainable it is 
highly desirable that some method of heating be devised Avhereby coal 
can be used, for this is a standard fuel which can be had in unlimited 
quantity. It seems possible that coal can be used for heating a sys- 
tem of 'flues if a forced draft is employed, but this would require 
some sort of motive power. 

BARNS ADAPTED TO THE USE OF HEAT IN CURING. 

It has already been pointed out that ventilation in conjunction 
with heat is required to control properly tlie humidity in the barn. 
The barns most used in curing shade-grown tobacco are high and 
have a steep shingle roof. Air can penetrate the shingle roof rather 
freely, which makes it possible to utilize charcoal fires without the 
use of a roof ventilator, but, nevertheless, the curing conditions could 
be better controlled with such a ventilator. In curing with flues, 
especially in the case of tobacco other than shade grown, the leaf of 
which is much larger and heavier in body, the roof ventilator is very 
important. Moreover, lower barns with flat roofs are much more 
desirable, for it is very difficult to force the heat through the green 
tobacco in liigh barns with steep roofs. Moderate-sized barns aaIucIi 
can be filled in a day or two, so that the heat can be a])plied promptly, 
are preferred to larger ones. In the case of large l)arns, however, 
to iill which requires several days, temporary i)artitions can be put 
in at convenient intervals by tacking up strips of burlap on the 
cross framing. Tlie burlap partitions, wdiich are \evy effective in 
preventing the escape of the heat, make it possible to run the fur- 
naces in one section while the next is being filled. 

In figure 4 is shown a 7-bent barn with a low, flat roof of paper, 
designed by Mr. W. S. Pinney, of Suffield, Conn., which is especially 
adapted for curing the ordinary types of picked wrapper leaf. It 
will be noted that in addition to the regulation side ventilators a 
special ventilator extends along the peak of the roof, which opens on 
each side. The doors on either side can be opened or closed from 
the ground by means of ropes and pulleys, "V'Nliile heat is being 
applied all side ventilators are tightly closed, except the horizontal 
ventilator at the bottom, through which such air as is needed for 
ventilation is introduced. In operating the roof ventilator the prin- 
cipal point to be observed is to open only the side away from the 
wind. In diy Aveather comparatively little ventilation will be needed 
and frequently none at all, while in wet weather amjde opportunity 
for the circulation of air niust be given. 

The aim should be to allow the air to enter the lini'ii near the ground 
and, after being heated by coming in contact with the flues, to pass 
upward through tlie tobacco and finally to pass out through the roof 
N'entilator. This is in accordance vith natural laws regulating th.e 

241 



24 USE OF ARTIFICIAL HEAT IN CURING CIGAR-LEAF TOBACCO, 

circulation of air as affected by temperature. The sole object is to 
so regulate the heat and ventilation as to secure the proper tempera- 
ture in the barn for curing and so to control the humidity that the 
tobacco will not be injured by drying either too rapidly or too slowly. 




Fig. 4. — Moderate-sized barn with low, flat roof and ventilator extending along the peak 
of the roof, especially adapted for the use of artificial heat in curins;. 

We have here outlined a means for accomplishing this object, which 
makes it possible to cure cigar tobacco under uniformly favorable 
conditions regardless of the outside weather. 

SUMMARY. 

Methods of curing have not kept i)ace with the advances made in 
other features of cigar-tobacco production and are still comparatively 
crude. Curing involves important changes in the composition of the 
leaf other than the loss of water, and a clear distinction is to be made 
between curing and mere drying. The process is dependent on the 
life activities of the leaf cells and is essentially a process of starva- 
tion. 

To insure good curing, the leaf tissue must not be killed or in- 
jured by freezing or by bruising before being placed in the barn, the 
temperature in the barn must be moderately high, and the rate of 
drying must not be too rapid during the first stages of the process. 

The disease known as pole-sweat, which is merely a decay of the 
leaf, is due to excessive moisture in the barn after the leaf has been 
yellowed. This disease can be readily controlled by the combined 
use of heat and ventilation. 

The application of artificial heat under proper conditions does 
not injure the quality of cigar tobacco, but on the contrary insures 
better curing, especially as regards the color of wrai)per leaf. It 
has given particularly good results with picked or primed tobacco. 

241 



SUMMARY. 25 

To apply artificial heat effectively and economically requires a 
reasonably tight barn, and adequate ventilation must be provided 
to control properl}' the humidity. The heating system should have 
sufficient capacity to maintain in the barn a temperature from 15 
to 20 degrees above that of the outside air. 

Open charcoal fires are used successfully in curing shade-grown 
tobacco, but charcoal is an expensive fuel, the supply is limited, and 
properl}^ to care for the large mnnber of fires required is a laborious 
task. This method of applying heat would be decidedly more ex- 
pensive in the case of ordinary ^^icked or primed tobacco and when 
tobacco is cured on the stalk. 

A method has been devised for applying artificial heat by means 
of a system of furnaces and flues in which wood is used as fuel. In 
this method a furnace and set of flues are required for each '' bent " 
or IG-foot section of the barn. An important feature of the system 
is a ventilator extending along the peak of the roof. Details regard- 
ing the construction and use of this system have been outlined. It 
has been fully demonstrated by tests conducted on a large scale that 
this method gives excellent results in curing, especially in the case 
of tobacco harvested by picking the leaves from the stalk. 

Moderate-sized bams with low, flat roofs, which can be completely 
filled with tobacco in one or two days, are best adapted to the use 
of artificial heat in curing. 

241 



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